Heretofore, there is disclosed a wrist mechanism which comprises, at the front end portion of the arm of an industrial robot, a rotary shaft rotating about a second axis perpendicular to a first axis extending in a length direction of the arm and a rotary shaft rotating about a third axis perpendicular to the second axis, wherein two drive mechanisms for independently driving the second and third axes are provided, thus to thus rotate a tool fixing portion through a bevel gear about the second and third axes (e.g., Japanese Utility Model Application Laid Open No. 70896/1988).
Moreover, there is disclosed a wrist mechanism in which an arm is formed by three shafts of a the hollow structure in a concentric form. An inclined rotary portion in a hollow form rotating through a hollow bevel gear about a second axis inclined relative to a first axis extending in a length direction of the arm is provided at the front end portion thereof, and a hollow tool fixing portion rotating through a bevel gear about a third axis inclined relative to the second axis is provided (e.g., (Japanese Patent Application Laid Open
However, in the prior art of the aforesaid Japanese U.M. application Laid Open No. 63-70896, since the front end portion of the arm is occupied by two drive mechanisms for independently driving the second and third axes, cable and hose for supplying electricity and fluid such as pressurized oil or pressurized air, etc. cannot be passed through the tool fixed at tool fixing portion, and such cable and hose are therefore disposed outside the wrist portion. For this reason, there was the problem that in the case where the wrist portion is rotated many number of times, cable or hose is wound around the wrist portion, so the rotational operation range of the wrist portion is limited.
Moreover, in the prior art of the aforesaid Japanese Patent Application Laid Open No. 61-168487, while cable or hose can be passed through the hollow arm, it is necessary to pass such cable or hose inside three hollow bevel gears of the wrist portion and the hollow passage is curved. And there was the problem that at the time of performing the work for attachment/detachment of the cable or hose, the tool is detached from the tool fixing portion and connector is then detached, so it would take much time.